1. Field of the Disclosure
This disclosure relates to a microphone (e.g., electroacoustic transducer), and more particularly to a dynamic boundary pressure zone microphone assembly for musical instruments and sound reproduction, in which a transducer mounted in a baffle is statically mountable in close proximity to a vibrating membrane, such as the head of a banjo, the top or back plate of a guitar, violin, viola, cello, bass, mandolin, drum, or piano, or any other musical instrument with a vibrating membrane as a sound producing element, e.g., a primary sound producing element.
2. Description of the Related Art
A major problem with the current way in which microphones are used with musical instruments is that at the distances the microphones are commonly arranged at relative to a sound source (e.g., 3″ to 12″ from a sound source), acoustic feedback is a constant problem. Also with the use of some microphones, there may be a natural bass boost as the musician brings an instrument closer to the microphone (what is called the “proximity effect”). These two issues can severely limit the loudness one can achieve with a microphone on stage.
Audio feedback (also known as acoustic feedback, simply as feedback, or the Larsen effect) is a special kind of positive loop gain which occurs when a sound loop exists between an audio input (for example, a microphone or guitar pickup) and an audio output (for example, an power amplified loudspeaker). In this example, a signal received by the microphone is amplified and passed out of the loudspeaker. The sound from the loudspeaker can then be received by the microphone again, amplified further, and then passed out through the loudspeaker again. The frequency of the resulting sound is dependent upon resonance frequencies in the microphone, amplifier, and loudspeaker, the acoustics of the room, the directional pick-up and/or emission patterns of the microphone and loudspeaker, and/or the distance between them.
Feedback is almost always considered undesirable when it occurs with a singer's or public speaker's microphone at an event using a sound reinforcement system or PA system. Audio engineers may use highly directional cardioid microphones (e.g., super cardioid and hyper cardioid microphones) and various electronic devices, such as equalizers and, since the 1990s, automatic feedback detection devices to prevent these unwanted squeals or screeching sounds, which can detract from the audience's enjoyment of a performance.
For example, a conventional microphone placed on, or a few inches above, a hard boundary surface will pick up the desired direct sound as well as delayed sound reflecting off the boundary surface. The direct and delayed reflected sounds will combine at the microphone to create comb filtering, with constructive and destructive interference causing undesirable peaks and valleys in the frequency response. The delay time of the reflection for most microphones may be in the range of 0.1 to 1 milliseconds, corresponding to cancellation frequencies of a few kilohertz and octave multiples. Since these frequencies are audible, the cancellation effects are also audible and are said to undesirably “color” the resulting audio signals.
With a pressure zone (or boundary) microphone, however, by placing the diaphragm of the microphone capsule parallel to and facing the plate boundary provided by the microphone package, the reflected sound delay is reduced, and the resulting comb filter interference frequencies are high enough that they are outside the audible range. Thus, a main advantage of boundary microphones is the elimination of interference from reflected sound waves. As explained, a normal microphone will pick up sound waves from the primary source and also any reverberations, which can result in unnatural sound reproduction. In the pressure zone microphone, however, sound waves are in phase and there is no (or little) interference.
Conventional boundary microphones, however, are set at a boundary of a surface of a room or a surface in the room for pickup of much more distant sound sources (using the wall as the baffle). For example, conventional boundary microphones work best when placed against a hard, flat surface at least one meter square; for example, a tabletop or wall. Additionally, some boundary microphones use a large reflective baffle to simulate a wall. In some cases, large reflective baffles are built into the microphones, and in other cases, the boundary microphones are used on conference tables (which act as the baffle). While some pressure zone microphones are used for micing instruments, these treat the whole instrument as the “room.”
Therefore, there is a need for an improved pressure zone (or boundary) microphone that may be used with an individual instrument.